Polyimides, such as those described in Edwards, U.S. Pat. No. 3,179,614, can be used in a wide variety of commercial applications. The outstanding performance characteristics of these polymers under stress and at high temperatures have made them useful in the form of bushings, seals, electrical insulators, compressor vanes and impellers, pistons and piston rings, gears, thread guides, cams, brake linings, and clutch faces.
It is often desirable to incorporate various additives in such polyimide compositions before fabrication into their final form. Accordingly, graphite has been incorporated to improve the wear characteristics in bearing applications. Diamonds have been incorporated for abrasive applications. Fluoropolymers have been incorporated in the past for lubricity in forming and extrusion of shapes.
Despite the variety of polyimides and additives that have previously been available, a continuing need for polyimide compositions, particularly when processed into the shape of bushings and bearings, is a reduction in the thermal expansion of such materials. In bushings and bearings, close clearances to adjacent metal surfaces are needed, in combination with excellent wear characteristics. In the past, while additives could be incorporated for the reduction of wear, it has previous not been possible to prepare a polyimide composition having both low wear and friction performance and a low coefficient of thermal expansion.